In recent years, the widespread availability of camera phones having a camera function has increased the opportunities for users to photograph various kinds of photographic subjects. For example, a photographic subject at a distance from the camera lens, such as a friend or scenery, is photographed (normal snapshot) or a photographic subject at a close distance from the camera lens, such as a bus time schedule or flower petals, is photographed (close-up photography).
For close-up photography (macro photography), the camera lens needs to be positioned slightly closer to the photographic subject than for a normal snap shot. Therefore, a photographing lens system of this kind is equipped with a drive mechanism that drives the lens to be displaced in the optical axis direction; by switching a switch, the drive mechanism is driven to move the lens in the optical axis direction (see Patent Reference 1: Japanese Patent Application 2005-37865, for example).
The lens driving device disclosed in Patent Reference 1 comprises a lens holder equipped with lenses, a movable body for holding the lens holder, and a fixed body for supporting the movable body to move in the optical axis direction. In the lens driving device of Patent Reference 1, a magnet is attached to the movable body and a drive coil is attached to the fixed body. However, there are lens driving devices in which a drive coil is attached to the movable body and a magnet is attached to the fixed body.
As for the latter lens driving device, an adhesive is generally used for adhering the magnet to the fixed body (a cover portion). In order to heat-harden the adhesive, the manufacturing process of the lens driving device includes the step of placing the magnet and the fixed body in a high temperature room.
However, once the magnet is placed in a high temperature room, its magnetism may be deteriorated due to high temperature depending on the conditions; as a result, the thrust force for moving a movable body may be deteriorated. One may think that if a larger magnet is used, the influence of the deteriorated thrust force is minimized even if magnetism is deteriorated somewhat. However, the demand for smaller lens driving devices has increased and it is difficult to solve this problem by simply enlarging the magnet and the entire lens driving device.
At least an embodiment of the present invention, then, is devised considering the above problems, and provides a lens driving device having improved thrust force for moving a movable body.